The invention relates to solid waste conversion and energy production facilities, and in particular to power plants that are specially adapted for conversion of solid municipal and industrial waste into carbonaceous fuel and other marketable products and the use of such fuel in electricity generation. Such plants that have zero or substantially reduced airborne pollution emissions are especially relevant.
Approximately ninety percent of the carbon-based waste produced in industrial societies is interred in land fills. Disposal of municipal and industrial solid waste has become a major issue due to space limitations for land fills. Land fill interment adds to environmental pollution and the energy contained therein is lost to human use. Industrial use of this wasted energy could significantly impact dependency on fossil fuels. Some waste materials, such as human medical waste, pose public health problems that require their destruction, e.g. by incineration, rather than disposal in a land fill. Gasification of municipal, industrial and medical solid waste material by conventional means, such as incineration and pyrolysis, results in airborne emissionsxe2x80x94primarily nitrous and sulfurous gases (NOx and SOx), ash and other suspended particulate matter (PM), and partially-burned hydrocarbons (HCs), with the mix and amounts of the different pollutants depending on the type of plant, the particular solid waste input into the plant, and the efficiency with which it consumes the solid waste material. Such pollution has frequently resulted in local opposition and site location zoning problems for new waste incineration or pyrolysis facilities.
Approximately sixty percent of the electricity generated in the United States comes from the burning of coal and oil, while another ten percent is produced from burning natural gas. The burning of these fossil fuels releases carbonaceous (CO, HCs) and nitrous gases (NO, NO2, NO3, HNO2, etc.), as well as sulfur dioxide (SO2), into the atmosphere, contributing to urban smog, although usually at lower levels than the aforementioned conventional solid waste burning plants. The operations of many fossil fuel electrical generating plants, particularly coal burning plants, are restricted to a certain number of hours per day, because full-time operation would otherwise exceed legal pollution limits.
Conventional industrial furnaces, used to produce heat and electrical power for manufacturing processes, also emit flue gases into the atmosphere.
A major source of air pollution is nitrogen oxides (NO, NO2, NO3, HNO2, etc.). Ambient air is composed of 79 percent nitrogen, and nitrogen oxides are commonly contained in flue gases resulting from open-air combustion processes. For readily combustible fuels, like natural gas, the formation of nitrogen oxides can be reduced, but not eliminated entirely, by using a lean fuel-to-air ratio. Flue scrubbers can be incorporated into plants to remove nitrogen oxides (as well as SO2 and other pollutants) from the exhaust prior to release into the environment.
In U.S. Pat. No. 6,066,825, Titus et al. describe a system for generating electricity from the conversion of solid waste material into a gaseous fuel followed by combustion in a turbine or other generator. The conversion of the waste material involves a combination of an electric arc plasma furnace and a joule-heated melter. The plasma furnace is operated such that fast pyrolysis of the waste material occurs, creating a mixture of mostly CO and H2, with small amounts of CH4 and other light HCs, and a small amount of CO2. Non-gaseous components of the pyrolysis product are vitrified by the joule-heated melter into a highly stable glass product that can be disposed of safely or used commercially. The fuel gases are preferably combusted using a lean fuel-air mix in a steam-injected compressor-gas turbine or in an internal combustion engine, so as to produce electricity.
An object of the present invention is to provide an improved waste treatment and power production facility capable of converting solid waste materials to useful energy (heat and electricity) and marketable commercial products with zero air pollution emissions, the operation of which is largely or entirely self-powered.
The object has been met by a solid-waste energy plant containing a series of catalytic ionic-impact chambers to convert carbon-based waste material into fuel gas and also to regenerate the flue gases that are the product of combustion in turbine generators. The plant operates largely as a closed system to eliminate emission of flue gases into the atmosphere. Excess regenerated fuel and other useful waste conversion products can be separated and sold commercially.
The plant receives carbon-based waste material in a first catalytic ionic-impact chamber, which uses an electric arc to subject the waste material to homolytic bond cleavage, breaking the molecular bonds and leaving a plasma gas, which then recombines into simple molecules of H2, CH4, CO, CO2, S2, H2S, etc. The exact mix of resultant gases depends upon the composition of the waste material input into the chamber and choice of operating parameters, but it is mostly H2 and CO, and is a medium grade fuel gas. The sulfurous components, if present, are removed by a scrubber and the elemental sulfur sold commercially, as is any glassy or metallic slag material recovered from the bottom of the first chamber. The scrubbed gas can be further energized by passage through a second ionic-impact chamber filled with incandescent coke (derived from high-carbon waste, such as shredded rubber tires). There, H2O is converted to H2 and CO, while CO2 is converted to CO, through reaction with the carbon in the incandescent carbonaceous materials. After combustion of the energized fuel gas in a turbine, which generates electricity for the plant, the flue products of CO2 and H2O are cycled to another ionic-impact chamber, also filled with incandescent coke, for regeneration back into medium grade fuel gas of H2 and CO. Excess gases may be converted in yet other ionic-impact chambers to H2 and CH4 and sold commercially. Excess CO2 could also be sold.
In this way, solid waste material that would otherwise be disposed in landfills is converted into fuel for energy generation. High-carbon wastes, like rubber tires, which are normally difficult to convert directly into gaseous fuel in arc plasma chambers because of their relatively low oxygen content, are used for flue gas regeneration and thereby effectively converted into energized fuel gas. The energized fuel operates turbine generators for supplying the electric power for the electric arcs that heat the reaction chambers, as well as for sale of the excess electricity generated. The zero-emission closed system eliminates air pollution, as all products are extracted for commercial sale.